IMHO units are quite relative. As long as you stay in the Poser environment, it does not really matter whether 1 Poser unit equils 1 inch or feet or meter. Sometimes things matter at import or export.

Things change when you want to relate the poser universe to something in the real world. This mainly happens in the Dynamics, especially the cloth parameters.
These are in semi-metrics; cm (instead of meter), grams (instead of kg) and frames (instead of sec, 1 sec = 30 frames even when you say it's 25 in your animation).
When you switch units in Poser, these parameters do not change accordingly.  Density 0.1 means 0.1 gram/cm2 even when you set inches as the internal unit.

Hence, when you do calculations on animation combined with cloth room, working in metrics might save you from unit conversion issues. 

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though